In recent years, synthetic resin containers composed of polyethylene terephthalate (PET bottles) have come into common use as beverage containers. Synthetic resin containers have the advantageous properties of being light and shatterproof in comparison with conventional glass bottles.
Additionally, as caps for this type of synthetic resin container, metallic caps of aluminum alloy or the like have been conventionally used. Using synthetic resin caps in place of these types of metallic caps has also been considered.
With regard to these types of synthetic resin caps, those disclosed in Japanese Patent Application, First Publication No. Sho 62-251352 and Japanese Patent Application, First Publication No. Hei 2-296666 are known.
These conventional synthetic resin caps are screwed onto containers having an external thread formed on the mouth portions and annular expanded portions below the external thread; the caps are composed of a synthetic resin cap main body formed by a top plate portion and a tubular portion which extends downward from the peripheral portions thereof, and a thin liner provided on the inner surface of the top plate portion of the cap main body, the cap main body being such that the bottom portion thereof is partitioned, by means of a horizontal score formed around the circumference while leaving a plurality of thin bridges, into a main portion above the horizontal score and a tamper-evidence ring portion below the horizontal score. A threaded portion for screwing onto the external thread on the mouth portion of the container is formed on the inner wall surface of the main portion of the cap main body, and multiple wings or tabs are provided so as to be erectable on the inner wall surface of the tamper-evidence ring portion.
Additionally, as the containers, those having an external thread formed on the outer circumference of the top end portion of the mouth portion and provided with an annular expanded portion (locking ring) below the external thread are used.
With these types of caps having tamper-evidence properties, it is preferable that the relationship between the seal release angle, hereinafter abbreviated to SRA, and the bridge breaking angle, hereinafter abbreviated to BBA, be held to be such that SRA-BBA=0 degrees or greater, more preferably +30 degrees or greater, wherein SRA is the rotational angle at the moment the seal of the container is released due to the top end of the mouth portion of the container being separated from the inner surface of the cap or the liner when the cap attached to the mouth portion of the container is rotated from the initial position in the direction of opening, and BBA is the rotational angle at the position where the bridges are broken when the cap attached to the mouth portion of the container is rotated from the initial position in the direction of opening. That is, it is desirable, when opening the cap, that the bridges are broken before the seal is released due to the top end of the mouth portion of the container being separated from the liner or the like.
However, with the above-mentioned synthetic resin caps, there are cases wherein the bridges formed from synthetic resin expand and the engaging projections (wings or tabs) are so soft as to bend when engaging with the annular expanded portion, as a result of which the BBA can increase and SRA-BBA can become less than 0 degrees; thus, there are points requiring improvement from the point of view of tamper-evidence properties.
Techniques for separating a cap main body and a tamper-evidence ring portion with a small rotational angle in order to enhance tamper-evidence properties are disclosed, for example, in Japanese Patent Application, Second Publication No. Sho 32-1945.
As sealing devices designed to increase the above-described tamper-evidence properties using synthetic resin caps, those described in Japanese Patent Application, Second Publication No. Hei 3-56990 are known. These sealing devices comprise engaging claws having engaging side edges extending downward with a tilt in the cap-opening direction underneath the external thread of the container, and engaged claws which cooperate with the above-mentioned container engaging claws formed on the inner walls of the tamper-evidence ring portion of the cap. With the sealing device of Japanese Patent Application, Second Publication No. Hei 3-56990, when the cap is turned in a cap-opening direction with the cap attached to the mouth portion of the container, the engaged claws formed on the tamper-evidence ring portion are guided to the tilted engaging side edges of the engaging claws so as to be forced downward, and the tamper-evidence ring portion is forced to move downward to accelerate tearing along the tear line formed on the cap tubular portion.
However, in these conventional sealing devices, since the engaged claws formed on the cap have a fixed structure such as not to bend, the engaged claws on the cap must be forced past the engaging claws on the container when the cap is attached to the container, so that the plurality of bridges which couple the main portion of the cap tubular portion with the tamper-evidence ring portion must be reinforced to some extent, as a result of which the resistance to breakage of the bridges when the cap is opened is large and the seal cannot be easily opened. Additionally, in order to prevent the bridges from breaking when the cap is attached to the container (when the container is sealed), the tamper-evidence ring portion could be given an engaging structure for preventing relative movement in the cap-closing direction, but this presents a problem in that it would become difficult to mold the cap and the costs would increase. Furthermore, since these containers according to the conventional art are for engaging side edges of the engaged claws having fixed structures such as not to bend, these containers cannot be applied to caps provided with multiple wings or tabs which are erectable on the inner wall surface of the tamper-evidence ring portion as described in Japanese Patent Application, First Publication No. Sho 62-251352 and Japanese Patent Application, First Publication No. Hei 2-296666. That is, with the structure of the container described in Japanese Patent Application, Second Publication No. Hei 3-56990, only engaging claws having engaging side edges extending downward while tilting in the cap-opening direction are formed underneath the external thread, so that when the above-mentioned cap having the wings or tabs is attached and the cap is turned in a cap-opening direction, the wings or tabs contact the tips of the engaging claws, the tips of the wings or tabs are bent upward, allowing the engaging claws to pass without engaging the engaging claws, as a result of which the cap can be removed without breaking the bridges.
Additionally, as another example of conventional art, those described in Japanese Patent Application, First Publication No. Hei 7-291317 have been proposed.
The sealing device described in this publication comprises an external thread on the mouth portion of the container, an annular chin portion positioned therebelow, and ratchet claws positioned therebelow spaced along the circumferential direction. An internal thread is formed on the inner circumferential surface of the main portion of the tubular portion of the synthetic resin cap, and engaging flaps which extend upward at an incline in the radial inward direction from the base end are formed on the inner circumferential surface of the tamper-evidence ring portion spaced in the circumferential direction.
When this type of sealing device formed by combining a container with a cap has the mouth-neck portions sealed by attaching the cap to the mouth portion of the container, the rotation of the cap in the cap-opening direction, not the movement in the upward direction, is inhibited due to the side edges in the circumferential direction of the engaging flaps formed on the tamper-evidence ring portion of the cap contacting the rear surfaces of the ratchet claws which extend at a steep incline.
That is, the conventional sealing device composed of a synthetic resin cap and a container as mentioned above has a formation wherein, when the cap attached to the mouth portion of the container is turned in the cap-opening direction, the engaging flaps formed on the inner circumferential surface of the tamper-evidence ring portion of the cap are engaged with the ratchet claws formed on the mouth portion of the container to inhibit the rotation of the tamper-evidence ring portion in the cap-opening direction, as a result of which a force in the rotational direction is directly applied to a plurality of bridges which couple the main portion of the cap tubular portion with the tamper-evidence ring portion to break the bridges.
However, with regard to the above-mentioned conventional sealing devices, since the bridges are severed by pulling apart the plurality of bridges at once, there is a risk that the rupture resistance of the bridges could increase so that the bridges are not sufficiently severed, or that the engaging flaps could be folded back due to the strong rupture resistance so as to pass the ratchet claws.
That is, in the weakened line of a cap tubular portion formed from a horizontal score cut along the circumferential direction of the tubular portion while leaving a plurality of thin bridges, each bridge has a thin pillar shape composed of synthetic resin. This type of bridge is comparatively easily stretched when a tensile force is applied in the longitudinal direction, and easily and reliably severs after a certain degree of stretching. However, when shear stress arising from the movement of the main portion which is turned in the cap-opening direction with respect to the fixed tamper-evidence ring portion is instantaneously applied to this type of bridge, the bridge has a high rupture resistance. In other words, tamper-evidence ring portions coupled to main portions by means of multiple bridges in this way are not easily torn even when a rotational force is applied in the cap-opening direction.
Additionally, with formations wherein bridges are severed according to conventional products as mentioned above, a large cap-opening torque is required in order to separate the tamper-evidence ring portion from the main portion, and this makes it difficult for children to open the cap. Additionally, even if one attempts to open the cap by applying a large cap-opening torque, this large force can be applied to the engaging flaps so as to cause the engaging flaps to be folded back and pass the ratchet claws, thereby making it impossible to separate the tamper-evidence ring portion.